. Bulletin - New York State Museum. Science. Fig. 81 Pyramidal group The general symmetry of this group is shown in fig. SI; as in the normal group the vertical axis is an axis of tetragonal sym- metry; a single plane of symmetry passes through the horizontal axes, which are not axes of binary symmetry as is the case in the normal group. The forms which have been described under the normal group occur also in the pyramidal group with the exception of the ditetragonal prism and pyramid. The relation between the symmetry of this group and that of the preceding one may be best studied by referrin
. Bulletin - New York State Museum. Science. Fig. 81 Pyramidal group The general symmetry of this group is shown in fig. SI; as in the normal group the vertical axis is an axis of tetragonal sym- metry; a single plane of symmetry passes through the horizontal axes, which are not axes of binary symmetry as is the case in the normal group. The forms which have been described under the normal group occur also in the pyramidal group with the exception of the ditetragonal prism and pyramid. The relation between the symmetry of this group and that of the preceding one may be best studied by referring to fig. 82 which shows the ter- mination of a pyramidal crystal. The absence of vertical planes of symmetry, characteristic of this group should be noted. Two new forms occur, namely: prism of the third order, repre- sented in fig. 84; pyramid of the third order, represented in fig. 83 by the faces marked x. The relations of the pyramid and prism of the third order. Fig. 82. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original New York State Museum; New York State Museum. Albany : New York State Education Dept
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